Luminaire



jam, B945. K. FR

ANCK

LUMINAIRE Filed Feb. 10 1943 3 Sheets-Sheet 2' TiETEa.

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ASVMMET/P/C FLTES Z6 INVENTOR //BT FRANCK www 2' ATTORNEY K. FRANCK Jan.23, 945.

LUMINAIRE 3 Sheets-Sheet 5 Filed Feb. l0, 1943 Patented Jan. 23, 1945LUMINAIRE Kurt Franck, Newark, Ohio, assignor to Holophane Company, Inc.poration of Delaware New York, N. Y., a cor- Application February 10,1943, Serial No..475,'3627 3 Claims.'

The present invention relates to luminaires and more particularly toluminaires of the type eniploying uorescent light sourcesand designed toproduce extensive light distribution.

The candlepower distribution designated usually as extensive allowsspacing of the units atv twice thev mounting height to produceuniformity of horizontal illumination on the. working plane. Withtheextended length of the` fluorescent lamp itis, of course, onlypossibleto produce a distribution of extensive character in the verticalplane at right angles to theaxis `of the lamp.

're Obtain extensive. distribution of iight from fluorescent lamps bylens actiondirectf light is caused to fall on a light spreading.- platesym-- metrical about a median plane, and wherein the 'prism surfaces tooneside of this plane spread alll the light possible away from the nadirto build up intensities .at higher angles, generally in the neighborhoodof 45. This divides the light so that except for the diiiusion in theplate and for the scattered reected light falling'V on the plate, thereis nothing to contribute brightness' on the portions of the surface ofthe plate remote from an observer stationed the dominant rays aredirected. As a consequence the plate doesnot light'up with completeuniformity over its entire surface. the plate nearer the observer lightsup Very uniiormly, but the remote half is not so well lighted andconsequently comparatively dull.

To improve the appearance of the plate it has been provided with shallowsymmetrical flutes which lspread the rays each side ofthe direction intowhich the general prismatic action sends them. As this generaldirectiony is in the neighborhood of 45 of the nadir there-is a tendencyfor these symmetric flutes to elevate some of the light too high, i. e.,into regions 60 above the nadir causing it to get into the glare zone.-

The present invention,l contemplates extensive lighting luminaires andlight4 transmitting' plates forfuse in the' same,v wherein the light iscontrolled in such a increase in the lmninousfarea of the plates and adiminution of the high Vangle diffused light so that the light is keptouto-f the. glare zone.

The present invention also contemplatesA che taining either oftheseresults singly.A

Other `and further objects will hereinafter appear as the .descriptionproceeds.

The accompanying .drawings show, for purposes of illustratingr the:presentinvention an embodiment in which the' invention in'av regiontoward which` The half f' way as to obtain a material may take torni,it-55 l 'plate is lighted' up- (Cl. 24U-106.1)

being understood that Athe;y drawings are illustrativer of the inventionratherr than; limiting: the

same.

In these'drawings:

Figure 1 dagrammatically illustratessa typical f extensive lightinginstallation: with; spacing of the luminaires twice the -mountingheight;

Figure 2 is a.diagrammatic'.view illustratingV a. typical extensivelighting distribution and'. the;

brightness aspects' ofthe-plate of usual construcf tion;

ing the: approach tothe ideal as' herein;

Figure. 3 isal crossr'seotionalview through the:

sources and lens plate showing. light control;

Figure 3a.Y shows ata greatlyyenlargedxscale:the; light controlofcertain'of the prismatic ribsand contrasts their contour with theprim'fartvcon-` tour;

Figure 4 is a View at. anenlarged: scale illustrating diffusion obtainedbyfi'lutes;

Figure 5 Ais adiagram illustratingtheA directional control at variouspointsfacross:thewidtlrof a' iiute; and

Figure 6 shows comparative curves of yrelative illumination results in ahorizontal plane.

A typical installation. o-f extensive lighting'A equipment isillustrated in Figure" 1 where themounting height' H ofthe luminairesIiswtwice the spacing D, i. eg, D=2Ha;ndthe angle'between" nadir. 'andthel rays fallin'gfmidway" between th'e-` luminaires is A's thisisthe'region hardest: to light by' reason of the. greater' distance'- f (1,41H) and the'angleofincidenceiitfis im;

portant to get'as f much light as possible inv the region approximately45above nadir.`

tures and contributes to glare.

Where the light output is divided in-thetypi'- cal manner illustratedbythe extensive 'distribue y tion photometric curve I0 'of Figure-2,' by-asimple I priorart prismatic plate' I'I whose' prism outline half of theplate so the right/half only appears tion of the arrow I4'.

The present invention makes itI possible to have,` ,j' tts-illustratedin Figure 2a, a; fairly `wide middle Figure 2a is a viewsimilarrtoFigure 2 illustrate! provided; for.

Higher angled light tends' to be wasted under'reniote xportion II6 of lthe plate I1 appear bright, whether viewed from the right or left of thecenterline I8, I8, this being diagrammatically illustrated by thearrowed lines in small rectangles I9, I9, which overlap in the regionI5-IS. The distribution curve is shown at I9'. To facilitate comparisonof values the curves I4' and I9' are at the same scale. In IS' there isan increase in candlepower in both beams. The reason for this increasein efficiency will be pointed out below.

In Figure 3 the plate I1 is assumed to be receiving the direct lightfrom two fluorescent lamps 20, whose centers yare in planes 2'20" asindicated. The overall width of the combined sources is approximatelyequal to the width of the middle portion I5-I6. Outside of points I5 andI6 the upper surface of the lens plate has regressed prisms 2| withactive surfaces 22 which concentrate rays such as 23, 24, 25, and renderthem substantially parallel in the refracting rnedlum at such anglesthat the emergent rays would be transmitted at an angle of approximately45 from the nadir, provided the lower surface of the plate were smooth.Such dominant ray directions are indicated by the lines 23', 24' and25'. The lower surface of the plate I1, opposed to prisms ZI, is,however, provided with small flutes 26 which are preferably asymmetric`as explained below.

The middle portion I5I6 of the plate is again divided into a centralportion I5'-I6 of a width substantially equal to the spacings 2Il'20 ofthe light source centers and portions I5-I5 and I6'I6 under the outerhalves of the lamps and intermediate the central portion and the' outeror marginal portions which are beyond I5 and I6, respectively. As shownin Figures 3 and 3a the plate has eight ridges or ribs 21a-21h,inclusive, in the left half of the central portion (IB-45') and fourridges or ribs 2li- 211, inclusive, in the left intermediate portionI5--I 5'.

The surfaces of the ridges 21a- 2171, inclusive, on the sides toward theplane Ill- I8 are active and have such slopes as to receive light, e.g., rays 29, 3D, 3I and 32, originating in portions of lamps 20--20between the planes 20'-26", and refract these rays away from the axisI8-IB in such directions that the dominant transmitted rays 29', 3l and32' are in directions generally parallel with the rays 23', 24', 25. Theleft faces of ridges 21a-21h, inclusive, are also active in divertinglight rays such as 35, 36 and 31 to-ward the right for transmission intothe right hand beam. Similar action takes place in the correspondingridges to the right of center line I8-I 8.

The ridges 21i-21l, inclusive (between I5' and I5) have active surfaceson the side toward center line I8-I8 which act on rays such as 28 fromthe nearer source and bend them away from the nadir for transmission asshown at 28', and also active surfaces acting on rays such as 34 andbending them to the right as shown at 34'.

Each ridge surface receives a bundle of subincidence i lof ray to thenormal to such a horistantially parallel rays from the source of a widthequal to the apparent width of the ridge. For example, ridge 21e may beassumed to receive (as indicated in Figure 3a) a bundle of rays 3l of awidth 3I`a and another bundle of rays 31 of a width 31a. Each bundlewill be divided into definite proportions depending upon the location ofthe apex of the ridge. Portions such as 3Ia' and 31a' strike therespective left and right active surfaces and are refracted with thedirections indicated by the arrows 3Ib and 31h, while portions 3Ia" and31a" strike the left and right surfaces, respectively, which for suchrays are substantially inactive. The ridge 211 receiving ray 28 dividesthe bundle of rays 28 of a width 28a as indicated at 28a' and 28a.

The ridge outline (21a,-21l') of prior art plate I I is shown in Figure3a by dotted lines superposed on the outline of the new plate. In theprior art plate a considerably greater portion of the bundle 3 Ia to theright of line 3 Iaa impinges on the surface near the center line and issent to the left, while a much 'smaller portion -of the bundle 31a. tothe left of line 31aa is intercepted by the left surface of the ridgeand transmitted through the plate. This left surface is in fact merely ariser to provide a connection from one active ridge surface to the nextwith proper mechanical strength. In the ridge outline in full lines theleft surface instead of being a mere riser handles a considerableportion of the light and transmits it in a direction to build up thebrightness of the plate. The action of the dotted prior art ridge(corresponding in position to 211) in dividing a ray bundle such as 28ais also indicated. There the contribution of the riser surface wasnegligible.

It will thus be seen that at each side of the axis I8, I8 there is asubstantial area of the plate wherein the ribs have supplemental actionwhich contributes light in a direction so as to cross the axis,therefore this area of the plate will appear bright when viewed from aposition on either side of the fixture. The lens plate therefore has amuch larger projected areal of uniform brightness. As more of the lenssurface is lighted up to increase the projected area of high brightness,

more luminous output is emitted in the directions under discussion. Theresultant increase in efflciency is obtained because in the region I5-I6the two beams (in both directions) can be generated as efliciently asone beam in one direction.

In practice the distance between the center lines of the lamps may bevaried within a considerable range, from that of the requirements ofmechanical clearance to the width separations within the limitationsimposed by considerations of efficiency of the entire light controlsystem which decreases when the lamps are spaced too far apart. Forpractical ranges of distance, the principle discussed in Figure 3 isapplicable.

Figure 4 illustrates asymmetric flutes 26 for altering the generalcontour which gives shape to a light transmitter. To analyze theoperation of the flute, its width is divided into four equal parts andlines 38, 39, 4D, 4I and 42 (to represent parallel rays originating onthe right hand side of the flute) are drawn at angles to the general(horizontal) contour such that if the bottom of the plate were smooth,as indicated by the dotted line 43, the light would be refracted so asto be emitted at an angle of 45 with the nadir. The angle of incidence iof ray 40 to the normal to such a. horizontal plane is such that theangle of refraction r of ray 40' would be 45 as indicated. Suchrefracted rays are indicated at 38', 39', 40', 4I' and 42',respectively, and it is obw'ous that throughout the width of the platesurface being considered there would be no diffusion and all the light(except losses) would be emitted at 45 to the nadir.

Each flute 26 in Figure 4 is composed of a cylindrical portion at theleft, or remote side, as indicated by the arc 44 struck about a centerat 45 to the left of the middle of the flute, and a plane portion at theright, or near side, as indicated by the tangent line 46. In thedrawings the rays '48 at point 52.

38--4.2, inclusive, are continued to the 'flute surface where it will beseen that the angle of incidence for 'the rays striking the -oonvex surLface diminishes from the value i near the point G to afsmaller Iangle iat -point Vvandthe angle of incidence for the `rays striking the yplanesurface is uniformly increased to i over theentire plane surface. Therefracted rays are indicated by the lines. 38a, 39a, 40a, Maand 42a,'respectively. 'Ilhe flutes 2li therefore introduce a diffusion asrepresented `by -the langle a -between rays 42a and 38a', rthe lightfrom 'the -plane portion being at higher angles and the light from 'theconvex portion being at lower angles than l'it would have come from theplane surface l43.

Figure 4 also shows 'by a dotted varc 4'41 the con-- tour of thesymmetric Viute used inthe central part of the plate of Figure 3Jthereby indicating the departure in contour -of the asymmetric -flutefrom a symmetric flute.

Figure 5 shows graphically at the various reference points E, F, G, H,I, on the fiat surface 43, the asymmetric flute 26 and the symmetricflute 41 the angle in degrees from the nadir at which the light is, orwould be, emitted. The horizontal line 48 at 45 from the nadir indicatesthe absence of diffusion for the rays from the smooth plate. The curvedline 49 shows that at point E the ray 38a is at an angle of about 33 tothe nadir, and that the angle continuously changes along the convexportion of the flute 26 up to the point of tangency with the line 46,where the maximum departure from the nadir of about 52 is achieved. Thisangle is retained over the plane area of the asymmetric flute asindicated by the horizontal line 50. This provides a denite upper limitto the angle into which the light can be diffused. The dotted line 5Ishows the diffusion from the comparison symmetric ute in which spread oflight is between about 38 and 60 from the nadir. The more highlyelevated light of the near edge of the symmetric flute is avoided by theasymmetric flute, and hence adequate diffusion may be had withoutbuilding up plate brightness in the region adjacent 60 from nadir.

Further analysis of Figure 5 shows that the solid curve representing theemission of light from the asymmetric flute intersects the horizontalline Reference point G divides the width of the flute in half. Thus thehorizontal distance from E to 52 is less than half and the horizontaldistance from 52 to I more than half. Accordingly, less light isdiffused downward below 45 than upward above 45. By scaling olf Figure 5the actual location of point 52, itcan be shown that about 45% of theincident light is diffused downward and upward; expressed differentlythis means that 20% more light is diffused upward than downward.

The ordinary symmetric flute does exactly the opposite. This is shown bypoint 53 at which the dashed curve, representing the emission from thesymmetric flute, intersects the 45 line a little to the right ofreference point G. This means that more light is diffused downward thanupward.

The asymmetric flute as shown on Figure 4 might well be considered as acombination of a flute and a prism.

The curved part generated by a radius around center 45, constitutes theute part and produces diffusion of the incident light. The straight lineportion extending on Figures 4 from `2t to 31 acts as a prism, elevatingthe beam without diffusing it.

'The result :of -thislelevation'is graphically shown on Figure 5 lby thehorizontal straight Iline ipertion vvof .the emission curve of theasymmetric figuration 'as 'shown between points 54 and 55. The fact thatline -54-55 is lhorizontal indicates that no diffusion is produced; thefact that it 'lies at about 253 :against nadir shows 'that `the beam iselevated Iby Aabout 8 above the 45 emission which would be obtained 4ifno lprismatic formationwere 1provided on the outside surface fof thelens.

Figure 6 illustrates the lcomparative output yof the luminaires ofFigures '2 and `r2a when spaced twice the mounting height. The relativehorizontal illuminations are given in percentage.-

With the earlier construction the illumination midway between theluminaireslwas about '64% of that immediately under them, as vshown inthe dotted line curve 160, while with the changed construction abovedescribed-the corresponding cur-ve 64I jindicates .approximately '80% ofthe maximum illumination over a wide area between the fixtures. Adifference such as 35% in illumination appears spotty to the eye, whilea 20% difference is not noticed.

Since it is obvious that the invention may be embodied in other formsand constructions within the scope of the claims, I wish it to beunderstood that the particular form shown is but one of these forms, andvarious modications and changes ibeing possible, I do not otherwiselimit myself in any way with respect thereto.

What is claimed is:

1. A direct lighting luminaire for producing an extensive lightdistribution with high output in regions approximately 45 above thenadir each side of a central median plane and having two adjacenthorizontal fluorescent light sources of substantial Width side by side,one on each side of said median plane, and a flat horizontal lighttransmitting plate substantially wider than the overall width of the twosources and disposed below the sources, the upper surface of the platehaving a central portion of a width substantially equal to the spacingof the light source centers,

and composed of longitudinally extending V shaped ridges wherein bothsurfaces of each ridge are active and receive light from both lightsources and are of such slopes as to refract it away from the nadir fortransmission from the lower surface of the plate at substantially 45angles above the nadir, the upper surface of the plate also havingintermediate portions extending laterally of the central portion andcomposed of longitudinally extending V-shaped ridges wherein bothsurfaces of each ridge are active and receive light from the nearersource and are of such slopes as to refract it for transmission atsubstantially 45 angles above the nadir, the upper surface of the platealso having marginal portions provided with longitudinally extendingregressed prisms of variant refracting power with active surfaces slopedin variant amounts for spreading away from the nadir light incidentthereon from the adjacent source for transmission from the lower surfaceof the plate at a substantially 45 angle above the nadir and inactiveriser surfaces receiving substantially no direct light from eithersource, whereby the area of brightness of the plate when Viewed ineither direction of the dominant light outputextends over thecorresponding marginal portion, the central portion, and bothintermediate portions.

2. A luminaire such as claimed in claim 1, wherein the lower surface ofthe plate has sym metric light spreading flutes opposite the central andintermediate portions for symmetrically diffusing light and hasasymmetric light spreading iiutes opposite the marginal portions forstrengthening the upward diffusion and limiting its angle from thenadir.

3. A direct lighting luminaire for producing an extensive lightdistribution with high output in regions approximately 45 above thenadir each side of a central median plane with controlled diffusionabove and below said 45 angle and having two adjacent horizontalfluorescent light sources of substantial width side by side, one on eachside of said median plane, and a at horizontal light transmitting platesubstantially wider than the overall width of the two sources anddisposed below the sources, the upper surface of the plate havingmarginal portions provided with longitudinally extending regressedprisms of variant refracting power with active surfaces sloped invariant amounts for spreading away from nadir light incident thereonfrom the adjacent source and rendering it parallel in the plate and atan angle to the normal to the horizontal plane corresponding with anangle of refraction of substan tially 45 from said normal, the lowersurface of the plate opposite said regressed prisms being composed oflongitudinally extending flutes, each ute having a downwardly convexportion disposed in the more remote portion of the iiute andr KURTFRANCK.

